Sullair LS-100 pressure relief

by Brendan
(MI)

I recently started a new job. Our facility has two Sullair compressors.

#1 (LS-10) has been running like a champ.

#2 (LS-100) had a hard time maintaining 100psi.

I gradually turned the regulator to get it up to the required pressure and it ran for about two days. The sump pressure was high and increased as time went on-blowing the pressure relief valve.

When I start the unit now, the sump pressure starts at 135 and rises rapidly-until the pressure relief valve opens.

The unit was recently PM’d. I have replaced the sump element as well as the oil and air filter, etc. The literature says replace sump element (done) or the regulator.

Is there something else that I should check before purchasing and replacing the regulator?

Thanks.

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Pressure relief valve or… ?
by: Doug in s.d.ca.

Pressure relief valve or blowdown valve?

“When I start the unit now, the sump pressure starts at 135 and rises rapidly-until the pressure relief valve opens.”

Starts at? Is it not at zero bar to start?

What are your set-points for low and high pressure?

Have you checked the separator since it was replaced? Is the filter screen in the scavenger line clear, and removing excess oil?

Is the inlet valve moving at all?

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My answers Sullair LS-100
by: Brendan

Sump pressure is zero when the unit is not running.

Pressure relief valve on the side of the sump tank-not the one on top.

110psi-100 psi.

I have not checked the separator since I changed it. It has less than 100 hours service time.

Filter screen appears to be clear.

I don’t know if the inlet valve moved.

This afternoon, I shut down #1 and started #2. It ran fine for a few minutes-sump pressure read 35. When system pressure dropped below 100psi she kicked in. The sump pressure raced up and was climbing when I shut her down.

Thanks,
B

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Pressure relief valve
by: Doug in s.d.ca.

“I don’t know if the inlet valve moved.”

You probably should try to find out, perhaps after you verify the pressure switch (further down).

“This afternoon, I shut down #1 and started #2. It ran fine for a few minutes-sump pressure read 35.”

135, I guess… but your sets are 110psi-100 psi, so it was running high already, right? Did it get to modulate, or just stop there until…

“When system pressure dropped below 100psi she kicked in. The sump pressure raced up and was climbing when I shut her down.”

Did you notice if the line pressure tracks the sump pressure? It should be pretty close.

If you haven’t, I think you should check the pressure switch. It may be either sick or maladjusted, or somehow not “seeing” line pressure.

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Thanks Doug
by: Brendan

Thanks for your time and patience Doug. I’m an electrician so my previous compressor experience has been to provide power, check the rotation, and let the pros take it from there.

Forgive me for not knowing the proper names of components and their functions, I know it makes it difficult to diagnose the issue.

I believe the inlet valve is moving, as system pressure falls to the cut in pressure, the motor sounds as though it takes on a mechanical load. It’s at this time that the sump pressure gauge goes from 35 to 175 (and climbing) in a few seconds.

I believe the pressure switch is functioning. It’s difficult to tell as line pressure never gets high enough for the compressor to cut off.

It’s as though air is entering the sump tank but not exiting. Is the minimum pressure/check valve the main outlet for the sump tank? Could that valve be stuck?

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MPV
by: Doug in s.d.ca.

“It’s as though air is entering the sump tank but not exiting. Is the minimum pressure/check valve the main outlet for the sump tank? Could that valve be stuck?”

Yes, and yes, though I can’t recall that happening. Stuck closed that is.

But 35 psi is where a typical MPV is set, so it’s probably sort of working, but maybe sticking when it needs to open wide under load.

Does this thing have a suffix like LS-100 HH or XH? And did you find a rating on/for the PRV on the side of the tank?

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’twas the poppet
by: Brendan

Thanks again Doug for your help.
In a desperation move, I opened the minimum pressure/check valve and removed the poppet. It looked a little oxidized(?) in some areas, I polished it with scotch-brite and closed the gap between the upper and lower segments. After reinstalling and reassembling it, I started the compressor and it worked fine.
Sump pressure is proportional to line pressure. Approximately 125psi sump pressure/ 110psi line pressure.
Should the two poppet segments move freely?
Should I replace that piece?

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Update
by: Brendan

Correction: Sump pressure is 110, as is line pressure.
I cannot see a suffix on the unit. it appears to be an LS-100.
The rating on the PRV is 200 psi.
Thanks.

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MPV
by: Doug in s.d.ca.

“Should the two poppet segments move freely?”
Not sure what you mean, but probably…

“Should I replace that piece?”

Depends. Are there decent maintenance records? How many hours on it?
Do you have the recommended repair kit?
If I were you, I think I might just keep an eye on it. What was the stuff you cleaned up? Color? Is this LS100 air or water cooled?

Do you/they run these alternately on some schedule, or is one or the other or both on-line depending on plant needs?

All that in aid of deciding whether to replace it immediately.

Anyway, good to hear it was a relatively easy (if perhaps temporary) fix.

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